CN112654579A - Hydraulic system for load handling vehicle - Google Patents

Hydraulic system for load handling vehicle Download PDF

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Publication number
CN112654579A
CN112654579A CN201980057452.4A CN201980057452A CN112654579A CN 112654579 A CN112654579 A CN 112654579A CN 201980057452 A CN201980057452 A CN 201980057452A CN 112654579 A CN112654579 A CN 112654579A
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CN
China
Prior art keywords
hydraulic
actuator
auxiliary
pump
load
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN201980057452.4A
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Chinese (zh)
Inventor
A·布鲁克克斯
P·利德利
T·麦卡恩
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Parker Hannifin EMEA SARL
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Parker Hannifin EMEA SARL
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Publication date
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Publication of CN112654579A publication Critical patent/CN112654579A/en
Pending legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/042—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in"
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/042—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in"
    • F15B11/0423—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in" by controlling pump output or bypass, other than to maintain constant speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/20—Means for actuating or controlling masts, platforms, or forks
    • B66F9/22—Hydraulic devices or systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/0401—Valve members; Fluid interconnections therefor
    • F15B13/0402—Valve members; Fluid interconnections therefor for linearly sliding valves, e.g. spool valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/14—Energy-recuperation means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/2053—Type of pump
    • F15B2211/20569—Type of pump capable of working as pump and motor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/30565—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve
    • F15B2211/3057—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve having two valves, one for each port of a double-acting output member
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/30585—Assemblies of multiple valves having a single valve for multiple output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3105—Neutral or centre positions
    • F15B2211/3116—Neutral or centre positions the pump port being open in the centre position, e.g. so-called open centre
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3122—Special positions other than the pump port being connected to working ports or the working ports being connected to the return line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3138—Directional control characterised by the positions of the valve element the positions being discrete
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3144—Directional control characterised by the positions of the valve element the positions being continuously variable, e.g. as realised by proportional valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/31505—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and a return line
    • F15B2211/31511—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and a return line having a single pressure source
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/31523—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and an output member
    • F15B2211/31541—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source and an output member having a single pressure source and multiple output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/31552—Directional control characterised by the connections of the valve or valves in the circuit being connected to an output member and a return line
    • F15B2211/31564—Directional control characterised by the connections of the valve or valves in the circuit being connected to an output member and a return line having multiple output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/3157—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line
    • F15B2211/31588—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line having a single pressure source and multiple output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/327—Directional control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/329—Directional control characterised by the type of actuation actuated by fluid pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/41—Flow control characterised by the positions of the valve element
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/41—Flow control characterised by the positions of the valve element
    • F15B2211/413—Flow control characterised by the positions of the valve element the positions being continuously variable, e.g. as realised by proportional valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/415—Flow control characterised by the connections of the flow control means in the circuit
    • F15B2211/4159—Flow control characterised by the connections of the flow control means in the circuit being connected to a pressure source, an output member and a return line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/42—Flow control characterised by the type of actuation
    • F15B2211/426—Flow control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/42—Flow control characterised by the type of actuation
    • F15B2211/428—Flow control characterised by the type of actuation actuated by fluid pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/46—Control of flow in the return line, i.e. meter-out control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/51—Pressure control characterised by the positions of the valve element
    • F15B2211/513—Pressure control characterised by the positions of the valve element the positions being continuously variable, e.g. as realised by proportional valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/52—Pressure control characterised by the type of actuation
    • F15B2211/526—Pressure control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/665—Methods of control using electronic components
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/665—Methods of control using electronic components
    • F15B2211/6651—Control of the prime mover, e.g. control of the output torque or rotational speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/80—Other types of control related to particular problems or conditions
    • F15B2211/88—Control measures for saving energy

Abstract

A hydraulic system (1, 50) for a load handling vehicle comprises a lifting actuator (2, C1) operating in a load lifting mode in which a load is induced on the actuator and a load lowering mode in which the actuator provides hydraulic power PI to the hydraulic system. An auxiliary hydraulic actuator (4, 6, 8, C2) is also provided, having a hydraulic power demand P2. The hydraulic pump (10, 58) directs hydraulic power to the hydraulic lift actuators and at least one auxiliary hydraulic actuator. The hydraulic system is configured such that hydraulic power can be directed from the hydraulic lifting actuators directly to the auxiliary hydraulic actuators when the hydraulic lifting actuators are in a load-lowering mode, requiring concurrent actuation of at least one auxiliary hydraulic actuator, and PI is greater than or equal to P2, such that the at least one auxiliary hydraulic actuator is fully actuated by hydraulic power from the hydraulic lifting actuators without the use of a pump.

Description

Hydraulic system for load handling vehicle
The present invention relates generally to hydraulic systems, load carrying vehicles such as electric forklifts, pickers and the like. More particularly, the present invention relates to an implement that utilizes hydraulic energy from a hydraulic lift actuator during load descent to power an auxiliary hydraulic function.
An electric load handling vehicle, such as an electric forklift or electric picker, includes an electric drive for providing movement to the vehicle and a hydraulic system, such as a lift circuit of a forklift, for powering a hydraulic actuator. Electric forklifts comprise a primary hydraulic actuator for vertically lifting the load. The main lift actuators are driven by hydraulic pump/motors through the main hydraulic circuit. When the main hydraulic actuator is operating at maximum load pressure, the main hydraulic circuit will typically be arranged to provide pressurized hydraulic fluid directly from the pump to the main actuator. In addition to vertical lifting of the load, the load handling vehicle will typically include auxiliary hydraulic actuators for performing additional functions, such as forward and rearward extension or lateral and/or transverse tilting of the load.
It is known to provide electric load handling vehicles with the ability to regenerate energy during a hydraulic drop in the load. In such systems, the hydraulic pressure induced during a load drop may be used to drive the pump/motor to operate as a generator to generate electrical power, which may be used to drive the vehicle or stored in the vehicle battery.
The master cylinder and the slave cylinder have different and often concurrent (simultaneous) fluid supply requirements. In current systems, if the helper cylinder is required to be used during load descent, the pump/motor must be operated to drive the helper cylinder and cannot be used for electrical regeneration. Energy from the master cylinder is lost to the reservoir. Certain systems are known that use the pressure of the descending load to boost the pump/motor when operating the helper cylinder, thereby enabling the pump/motor to operate more efficiently. However, this does not effectively recover energy from the falling load, and much of the energy is lost as heat.
Accordingly, it is desirable to provide an improved method and system for recovering hydraulic energy in an elevator car that is capable of efficiently recovering energy from a master cylinder while concurrently operating one or more auxiliary cylinders during a load drop, and/or that provides improvements generally.
In an embodiment of the present invention, there is provided a hydraulic system for a load handling vehicle, the system comprising: a hydraulic lift actuator arranged and configured to operate in a load lift mode and a load down mode in which a load is induced on the primary hydraulic actuator and the primary hydraulic actuator provides hydraulic power P1 to the hydraulic system; at least one hydraulic actuator having a hydraulic power demand P2 when operated; and a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator. The hydraulic system is configured such that when the hydraulic lifting actuators are in a load-down mode, at least one auxiliary hydraulic actuator needs to be actuated concurrently, and P1 is greater than or equal to P2, hydraulic power can be directed from the hydraulic lifting actuators directly to the at least one auxiliary hydraulic actuator such that the at least one auxiliary hydraulic actuator is actuated entirely by hydraulic power from the hydraulic lifting actuators without the use of a pump. In this mode of operation, no pump is required to drive the auxiliary actuator and no energy is drawn from the battery. The efficiency of the system is thereby improved by the hydraulic regeneration of the hydraulic power of the induced load which would otherwise be accompanied by a drop in the load and the introduction of fluid from the lift actuator to the tank, being wasted as heat of the hydraulic fluid.
The hydraulic pump is preferably a hydraulic pump/motor and is arranged to receive hydraulic power from the hydraulic lifting actuator when the hydraulic lifting actuator is in the load lowering mode. Further, the system may include a motor/generator and an electrical storage device. The motor/generator may be connected to the hydraulic pump/motor such that: in the drive mode, the motor/generator operates as a motor to power the pump/motor and the pump/motor operates as a pump, and in the regeneration mode, the pump/motor operates as a motor and drives the motor/generator to operate as a generator to generate electricity, which is supplied to the energy storage device. In this way, hydraulic power from the descending load may be used to provide electrical regeneration in addition to hydraulic regeneration, as operating parameters permit.
The hydraulic system is preferably configured such that when the hydraulic lifting actuators are in a load-lowering mode and it is desired to actuate the at least one auxiliary hydraulic actuator concurrently, and P1 is greater than P2, excess hydraulic power not required by the at least one auxiliary hydraulic actuator can be directed to drive the pump/motor in a regeneration mode. In this way, hybrid regeneration is allowed, wherein excess hydraulic power not used for hydraulic regeneration is used to drive electrical regeneration.
The hydraulic system preferably further comprises a reservoir tank and is configured such that when the hydraulic lifting actuator is in a load-down mode and it is desired to concurrently actuate the at least one auxiliary hydraulic actuator, and P1 is greater than P2, and regeneration is not desired, a surplus hydraulic flow from the hydraulic lifting actuator not required for the at least one auxiliary actuator is directed directly to the reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor.
The hydraulic system preferably further comprises a reservoir tank and is configured such that when the hydraulic lifting actuators are in a load-down mode and it is desired to concurrently actuate the at least one hydraulic actuator, and P1 is less than P2, hydraulic flow from the hydraulic lifting actuators is directed directly to the reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor and the hydraulic pump/motor operates in a drive mode to actuate the at least one hydraulic actuator.
The hydraulic system preferably further comprises a lift valve arranged to control a flow of hydraulic fluid to and from the hydraulic lift actuator, wherein the lift valve is operable to variably restrict the flow of fluid from the hydraulic lift actuator to the reservoir tank when the hydraulic flow from the hydraulic lift actuator is directed directly to the reservoir tank, thereby controlling the rate of descent of the hydraulic lift actuator.
Preferably, all of the hydraulic power P2 is directed to drive the pump/motor in the regeneration mode when the hydraulic lift actuators are in the load-lowering mode and operation of the at least one auxiliary hydraulic actuator is not required.
Preferably, when it is desired to concurrently operate the hydraulic lifting actuator in the load lifting mode and to operate the at least one auxiliary cylinder, both the hydraulic lifting actuator and the at least one auxiliary cylinder are driven by a pump/motor, which operates as a pump in the drive mode.
The hydraulic system preferably further comprises a lift valve for controlling flow to and from the hydraulic lift actuator and an auxiliary valve for controlling flow to and from the auxiliary hydraulic actuator, wherein when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and the load on the hydraulic lift actuator is greater than the load on the auxiliary hydraulic actuator, the auxiliary valve is throttled to generate sufficient back pressure to enable the hydraulic lift actuator to operate concurrently with the auxiliary hydraulic actuator.
Preferably, when the hydraulic lift actuators and the auxiliary hydraulic actuators are being driven concurrently by the pump/motors and the combined speed of the hydraulic lift actuators and the auxiliary hydraulic actuators exceeds the maximum speed of the pump/motors, operation of one of the hydraulic lift actuators and the auxiliary hydraulic actuators is prioritisation (priority) and allowed to continue operating at the required speed whilst throttling flow to the other to reduce the combined speed to a level at or below the speed range of the pump/motors.
Preferably, when the hydraulic lifting actuators are in the load-lowering mode and it is desired to concurrently actuate the at least one auxiliary hydraulic actuator, and P1 is greater than P2, but the lowering speed of the hydraulic lifting actuators is less than the demanded speed of the auxiliary hydraulic actuators, the hydraulic flow from the hydraulic lifting actuators may be directed directly to the reservoir tank such that it bypasses the hydraulic pump/motor, and the hydraulic pump/motor is operated in the drive mode to actuate the at least one hydraulic actuator.
In another embodiment of the present invention, a hydraulic system for a load handling vehicle is provided, the system comprising: a hydraulic lift actuator arranged and configured to operate in a load lift mode and a load down mode in which a load is induced on the primary hydraulic actuator; at least one hydraulic actuator; and a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator. The hydraulic system is configured such that a load induced on the hydraulic lifting actuators when the hydraulic lifting actuators are in a load-lowering mode and concurrent actuation of at least one auxiliary hydraulic actuator is required can be used to operate the at least one auxiliary hydraulic actuator.
In another aspect of the present invention there is provided a load handling vehicle, such as a forklift, comprising a hydraulic system as described above.
In another aspect of the invention, there is provided a method of operating a hydraulic system for a load handling vehicle, the hydraulic system comprising a hydraulic lifting actuator arranged and configured to operate in a load lifting mode in which a load is induced on the actuator and in a load lowering mode in which a main hydraulic actuator provides hydraulic power P1 to the hydraulic system, at least one hydraulic actuator having a hydraulic power demand P2 when in operation, and a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and at least one auxiliary hydraulic actuator, wherein, when the hydraulic lifting actuator is in the load lowering mode and the at least one auxiliary hydraulic actuator needs to be actuated concurrently and P1 is greater than or equal to P2, the method comprises the following steps: actuating the at least one auxiliary hydraulic actuator by directing hydraulic power from the hydraulic lifting actuator directly to the at least one auxiliary hydraulic actuator such that the at least one auxiliary hydraulic actuator is fully actuated by hydraulic power from the hydraulic lifting actuator.
The method preferably comprises: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than P2, excess hydraulic power not required by the at least one auxiliary hydraulic actuator is directed to drive the pump/motor in a regenerative mode to generate electricity.
The method preferably comprises: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than P2 and electrical regeneration is not required, an excess hydraulic flow from the hydraulic lift actuators that is not required by the at least one auxiliary actuator is directed directly to the reservoir tank so that it bypasses the hydraulic pump/motor reservoir tank.
The method preferably comprises: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one hydraulic actuator, and P1 is less than P2, directing hydraulic flow from the hydraulic lift actuators directly to the reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor, and operating the hydraulic pump/motor in a drive mode to actuate the at least one hydraulic actuator.
The method preferably comprises: when hydraulic flow from the hydraulic lift actuator is directed directly to the reservoir tank, the lift valve is operated to variably restrict fluid flow from the hydraulic lift actuator to the reservoir tank, thereby controlling the rate of descent of the hydraulic lift actuator.
The method preferably comprises: when the hydraulic lift actuators are in the load-down mode and operation of the at least one auxiliary hydraulic actuator is not required, all hydraulic power P2 is directed to drive the pump/motors in the regeneration mode.
The method preferably comprises: wherein when it is desired to concurrently operate the hydraulic lifting actuator in the load lifting mode and operate the at least one auxiliary cylinder, the pump is operated in a drive mode to drive both the hydraulic lifting actuator and the at least one auxiliary cylinder.
Preferably, the hydraulic system comprises a lift valve for controlling flow to and from the hydraulic lift actuator and an auxiliary valve for controlling flow to and from the auxiliary hydraulic actuator, and the method comprises: when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and the load on the hydraulic lift actuator is greater than the load on the auxiliary hydraulic actuator, the auxiliary valve is throttled to create sufficient back pressure to enable the hydraulic lift actuator to operate concurrently with the auxiliary hydraulic actuator.
The method preferably comprises: when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and the combined speed of the hydraulic lift actuator and the auxiliary hydraulic actuator exceeds the maximum speed of the pump/motor, prioritizing operation of one of the hydraulic lift actuator and the auxiliary hydraulic actuator and allowing said prioritizing operation to continue at the required speed and simultaneously throttling flow to the other to reduce the combined speed to a level equal to or below the speed range of the pump/motor.
The method preferably comprises: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than P2, but the rate of descent of the hydraulic lift actuators is less than the rate required by the auxiliary hydraulic actuator, directing hydraulic flow from the hydraulic lift actuators directly to the reservoir tank so that the hydraulic flow bypasses the hydraulic pump/motor, and operating the hydraulic pump/motor in a drive mode to actuate the at least one hydraulic actuator.
Control valve assemblies for use in the above hydraulic systems include load carrying vehicles, such as forklifts. The control valve includes a valve body having a bore and a spool (spool) located within the bore, the spool being axially movable along the bore between at least two operating configurations. A servo port is formed in the valve body and arranged for connection to a hydraulic consumer, such as a hydraulic actuator. A pressure port is also formed in the valve body and is arranged for connection to a hydraulic power supply, such as a pump. Additionally, a tank port is formed in the valve body and arranged for connection to a hydraulic tank reservoir. The valve is reconfigurable between first and second operating configurations. In a first operating configuration, the spool is configured and arranged to define a fluid path connecting the pump port, the servo port, and the tank port such that fluid is able to flow from the pressure port to the servo port and the tank port in a first flow direction and from the servo port to the pressure port and the tank port in a second flow direction, and the spool is controllable to variably restrict flow to the tank port. In a second operating configuration, the spool is configured and arranged to close the reservoir port and define a fluid path connecting the pressure port and the actuator port, and the spool is controllable to variably restrict flow between the pressure port and the actuator port.
The first mode of operation allows an off-load pump start-up in which the pump is operated without being loaded by lift pressure. The tank port will be fully open at start-up so there is no hydraulic restriction and the pump therefore operates under no load conditions. This arrangement avoids the need for a separate bypass valve as may be found in prior art arrangements. In addition, the ability to operate the spool to variably restrict the tank port in the first operating configuration enables opening flow to the actuator while also allowing unwanted excess fluid to flow to the tank when the flow demand of the actuator is less than the output flow of the pump when operating at the minimum manufacturer's suggested operating speed. By incorporating the functionality provided by the first and second operating configurations into a single spool valve, a significant improvement is provided over prior art arrangements that utilized multiple cartridge valves and significantly more complex control systems to provide the same functionality.
When the flow demand of the hydraulic actuator becomes greater than or equal to the minimum output flow of the pump, the spool may then be operated in a second operating configuration in which flow to the tank is closed and flow to the actuator is controlled by controlling the speed of the pump. The second operating configuration may also be used for energy regeneration purposes in case a flow through the pump is required during descent. The ability to operate the spool in the second operating configuration to variably restrict flow between the pressure port and the servo port enables control of flow from the actuator to the pump.
Preferably, the valve is reconfigurable to a third operating configuration in which the spool is configured and arranged to close the pressure port and define a fluid path between the servo port and the tank port, and the spool is controllable to variably restrict flow between the servo port and the tank port. This advantageously uses the flow from the actuator directly to the tank to achieve gravity descent. The ability to variably restrict the flow path allows control of the rate of descent. Incorporating the function realized in the third operating configuration into the spool valve provides a further advance over the prior art and eliminates the need for additional valve and control arrangements in the prior art that would otherwise be employed to realize the same function.
The valve spool is preferably configured such that: in a first operating configuration, the flow path between the pressure port and the servo port remains fully open when flow to the tank port is variably restricted.
Preferably, a controller is provided for controlling the axial position of the spool. The controller is thus configured to move the spool between the first, second and third operating configurations.
The control valve assembly may further comprise biasing means arranged to bias the valve spool into the first operating configuration. Thus, the first operating configuration with the tank port fully open is the default rest position of the valve spool. The controller operates the valve spool against the action of the biasing member to move the valve spool in the first operating configuration for variably restricting the tank port and to move the valve spool into the second and third operating configurations.
Preferably, in a first supply mode of operation in which the spool is arranged in the first operating configuration during activation of the pump, the reservoir port is open during pump activation to allow flow from the pressure port to the reservoir port. This corresponds to no flow to the fully unloaded start position of the actuator.
In a second supply mode of operation with the spool in the first operating configuration, the controller is configured to: when flow to the actuation port is open and the demand supply flow to the actuator is less than the minimum supply flow of the pump, the control spool proportionally closes the reservoir port to distribute flow between the actuation port and the reservoir port. In this case, the flow from the pump exceeds the demand of the actuator. Flow begins to the actuator and excess flow is directed to the tank.
In a third supply mode of operation, the controller may be configured to arrange the spool in the second operating configuration to close the reservoir port such that all flow from the pressure port is directed to the actuation port when the demanded supply flow to the actuator is equal to or greater than the minimum supply flow of the pump.
The controller is preferably configured to control the pump to increase in speed after the tank port is fully closed and the demanded supply flow to the actuator is greater than the minimum supply flow of the pump.
In a fourth supply mode of operation, the controller is preferably configured to arrange the spool in the second operating configuration and to throttle flow from the pump to the actuator by proportionally closing the flow path between the pressure port and the servo port when the required system pressure exceeds the demanded supply pressure to the actuator. This provides a simple and effective way of enabling the secondary actuator to operate at a higher pressure than the primary actuator
In a fifth regenerative lowering mode of operation, the controller may be configured to control movement of the spool to the second operating configuration to allow fluid to flow from the actuator to the pump. In this arrangement, the reservoir port is closed and a direct flow path between the actuator and the pump is created.
In a fifth regenerative descent mode, the controller is configured to control the spool to proportionally close a fluid flow path between the pressure port and the servo port to throttle flow from the actuator to the pump. This enables the flow to the pump to be limited, thereby preventing overloading of the battery during energy regeneration.
Preferably, in a sixth gravity-lowering mode of operation, the controller is configured to arrange the spool in a third operating configuration to allow fluid to flow directly from the servo port to the tank port when energy regeneration via the pump is not required.
In a sixth gravity-lowering mode of operation, the controller may be configured to throttle flow from the actuator to the tank by controlling the spool to proportionally close a fluid flow path between the servo port and the tank port to control lowering of the actuator.
The valve body preferably includes a pilot port arranged to receive pressurised fluid for controlling movement of the spool. The supply of pressurized fluid to the pilot port is controlled by a controller.
The control valve assembly may further include a proportional pressure relief valve connected to the pilot port for controlling fluid pressure at the pilot port. The proportional pressure reducing valve is controlled by a controller for controlling the supply of pressurized fluid to the pilot port.
The spool preferably includes a loading surface at a first end arranged such that pressurized fluid entering the pressure port exerts a force on the loading surface to cause axial movement of the spool in a first direction, and a biasing means is positioned at a second end of the spool and arranged to impart a biasing force to the spool in an axially opposite second direction.
A hydraulic control system for a load handling vehicle is also provided. The system includes a hydraulic actuator, a pump, a reservoir and a valve assembly as described above. A pump is fluidly connected to the pressure port of the valve, a hydraulic actuator is connected to the servo port, and a tank reservoir is connected to the tank port.
There is also provided a method for flow control of a load handling vehicle comprising a first hydraulic actuator, a pump, a tank reservoir and a valve assembly as described above. A pump is fluidly connected to the pressure port of the valve, a hydraulic actuator is connected to the servo port, and a tank reservoir is connected to the tank port. The method includes selectively moving the spool axially along the bore between the three operating configurations.
The method may further comprise: in a first supply mode of operation, the pump is activated with the spool arranged in the first operating configuration such that the tank port is open during pump activation to allow flow from the pump to the tank.
The method preferably comprises the following steps: in a second supply mode of operation, the control spool proportionally closes the reservoir port after pump activation to apportion flow between the actuator and the reservoir when the demand supply flow to the actuator is less than the minimum supply flow of the pump.
The method preferably comprises the following steps: in a third supply mode of operation, the spool when in the first operating configuration is controlled to close the tank port and direct all flow from the pump to the actuator when the demanded supply flow to the actuator is equal to or greater than the minimum supply flow of the pump.
The method preferably comprises the following steps: the speed of the pump is increased when the tank port is fully closed and the demanded supply flow to the actuator is greater than the minimum supply flow of the pump.
The load handling vehicle preferably further comprises at least a second hydraulic actuator supplied with fluid by the pump, the method further comprising: in a fourth supply mode of operation, the spool is arranged in the second operating configuration and is controlled to proportionally close the flow path between the pressure port and the servo port when the pressure demanded by the second actuator exceeds the demanded supply pressure to the first actuator, thereby throttling flow from the pump to the first actuator.
The method may further comprise: in a fifth regenerative lowering mode of operation, the spool is disposed in the second operating configuration to allow fluid to flow from the actuator to the pump.
The pump is preferably a pump generator, and the method may further comprise: the fluid flow from the actuator is used to drive and operate a pump generator to generate electricity.
The method may further comprise: the lowering of the actuator is controlled by throttling the flow from the actuator to the pump by proportionally closing the fluid flow path between the pressure port and the servo port.
The method may further comprise: the spool is controlled in a sixth gravity-down mode of operation to place the spool in a third operating configuration to allow fluid flow from the servo port to the tank port when energy regeneration is not required.
The method may further comprise: the lowering of the actuator is controlled by throttling the flow from the actuator to the tank by controlling the spool to proportionally close the fluid flow path between the servo port and the tank port.
The valve body preferably includes a pilot port, and the method further includes supplying pressurized fluid to the pilot port to control movement of the spool.
The invention will now be described, by way of example only, with reference to the following illustrative drawings, in which:
FIG. 1 is a circuit diagram of a hydraulic system;
FIG. 2 is a schematic illustration of a valve for use in a hydraulic system employing the present invention;
FIG. 3 is a schematic view of the valve in a first operating configuration;
FIG. 4 is a schematic view of the valve in a second operating configuration; and
FIG. 5 is a schematic view of the valve in a third operating configuration;
FIG. 6 is a schematic diagram of a hydraulic system according to the present disclosure; and
fig. 7 is a flow chart for operation of the hydraulic system of fig. 6.
Fig. 1 is a hydraulic circuit 1 for a load handling vehicle such as a forklift. The circuit comprises a main hydraulic actuator 2 which is connected in use to the lifting tines of a forklift truck which are movably mounted to the mast of the vehicle. The circuit also comprises a first auxiliary hydraulic actuator 4 arranged to perform an extending function in which the tines are moved forwards and backwards relative to the mast. The second auxiliary hydraulic cylinder 6 is arranged to tilt the mast of the vehicle to change the angle of the load in the forward and backward direction. The third auxiliary hydraulic cylinder 8 is arranged to move the tines sideways to the left and right relative to the mast. It will be appreciated that this is an example of one arrangement of auxiliary functions and that the circuit may include additional or fewer auxiliary hydraulic cylinders depending on the operating requirements of the vehicle.
A pump motor 10 is provided to operate the master cylinder and the slave cylinder. In a supply mode of operation, the pump motor 10 is configured to provide hydraulic flow/pressure to the hydraulic system 1 by rotating in a first supply direction and converting mechanical shaft power from the motor into hydraulic power. The pump motor 10 is also configured to operate in a regeneration mode in which the pump motor receives hydraulic flow/pressure from the system that causes the pump to rotate in a second regeneration direction. Hydraulic power is converted into mechanical shaft power, which can be converted into electrical energy. This bi-directional pump arrangement is known as a2 quadridant pump. The hydraulic system 1 further comprises a tank reservoir 12.
The first manifold 14 is configured to control flow from the pump 10 to the master cylinder 2. A second manifold 15 and a third manifold 17 are also provided to control flow to the helper hydraulic cylinders. The first manifold 14 includes a first pressure port 16 and a second pressure port 17. In the supply mode, the first pressure port 16 is an outlet port of the pump 10 and the second port 17 is a pump inlet that supplies flow from the reservoir 12 to the pump 10. The first pressure port 16 is connected via a flow passage 19 to a spool valve 18 configured as a smart distribution flow. The spool valve 18 controls the flow from the pump 10 to the first hydraulic actuator 2. The spool valve 18 is connected to the first hydraulic actuator 2 via a flow passage 22. A hydraulic load holding valve 24 is provided between the spool valve 18 and the first hydraulic actuator 2. The valve 24 is configured to operate in a deactivated position and an activated position. In the deactivated position, the valve 24 blocks flow from the first hydraulic actuator 2 to the spool valve 18, while allowing flow in the opposite direction from the spool valve 18 to the first hydraulic actuator 2. This enables the load on the first hydraulic actuator 2 to be held in place. In the activated position, flow can be transferred from the first hydraulic actuator 2 to the pump 10 or the reservoir 12.
An anti-cavitation check valve 20 is provided in the first manifold 12 as a safety feature. The fluid circuit further comprises an emergency lowering valve 23 configured to provide a throttled flow from the first hydraulic actuator 2 to the tank 12 for a safe lowering of the load in case of a system failure, e.g. an electrical failure in the control system.
A hydraulic pressure sensor 25 is provided to measure the load pressure on the forks. The hydraulic pressure sensor 25 may also be used as an input to the control system to further boost the control algorithm and optimize the activation/deactivation of certain hydraulic valves. A hydraulic shuttle valve 26 is also provided having inlet ports 28 and 30 and an outlet port 32. The valve 26 transmits the highest pressure from the two inlet ports 28 and 30 from the pump 10 or the first hydraulic actuator 2, respectively, to the outlet port 32, which supplies the spool 18.
Fig. 2 is an illustrative schematic view of the spool valve 18. The valve 18 includes a valve body having an axial bore and a valve spool 36 contained within the bore. The spool 36 is axially movable within the bore. Three operating configurations are represented schematically within the spool 36, which illustrate flow conditions with respect to the pressure port P, the servo port A and the tank port T in each of three operating positions corresponding to different axial positions of the spool along the bore. The spool 18 is pilot operated and a pilot port 40 is provided at a first axial end of the spool 36 arranged to receive fluid from the outlet 32 of the shuttle valve 26. Flow to the pilot port 40 is controlled by a Proportional Pressure Reducing Valve (PPRV)42 that proportionally varies the pressure at the pilot port 40 based on an electronic control signal provided to a coil within the valve 42.
The PPRV 42 is controlled by a controller that operates a control algorithm configured to control the position of the spool 36 based on the flow demand of the hydraulic system and current operating parameters. The pressure at the pilot port 40 acts on the spool 36 to axially move the spool 36 in a first axial direction away from the pilot port 40. At the opposite end of the spool 36 there is a biasing member 44 arranged to provide a biasing force in an axial direction opposite to the pilot pressure. The biasing member 44 may be a compression spring or any suitable biasing means. The biasing member 44 biases the spool 36 in a second axial direction toward the pilot port. To move the spool 36 in a first direction toward the biasing member 44, the pilot pressure must overcome the biasing spring force of the biasing member 44.
The valve body 34 comprises a pressure port P, a servo port a and a tank port T, the pressure port being connected to the pump 10 via a flow passage 19, the servo port being connected to the first hydraulic actuator 2 via a flow passage 22, and the tank port being connected to the tank reservoir 12. The spool 36 is configured to move axially between three different operating positions under control of a pilot signal. The spool 36 is configured to define different flow paths between the ports P, A, T in the three operating positions.
In the first operating position shown in fig. 3, the spool valve 18 is configured and arranged to define a fluid path connecting the pressure port P, the servo port a and the tank port T. In the first position, all three ports are connected such that fluid is able to flow in a first flow direction from the pressure port P to the servo port a and the tank port T and in a second flow direction from the servo port a to P and the tank port T. The spool 18, when in the first position, may be controlled by a pilot signal to variably restrict flow to the tank port T, as will be described further below.
In the first position, the spool 36 operates in a first mode of operation to facilitate the start-up of the no-load pump. In a hydraulic system, it is desirable that the hydraulic pump is started in an "unloaded" manner, which means that it is not loaded by the lifting pressure when the pump starts to rotate. In this way, the hydraulic pump can be rotated to a certain speed before the load pressure is introduced and gradually increased. In prior art arrangements, this is typically achieved using a bypass valve, but the inclusion of an additional bypass valve increases the cost and complexity of the hydraulic system. Due to the cost competitive nature of the forklift industry, bypass valves are often omitted from the hydraulic system. Thus, the hydraulic pump is started in a loaded manner without gradual introduction of a load, which results in premature wear of the hydraulic pump.
The first mode of operation of the spool valve 36 is controlled such that the pressure port P, the tank port T and the servo port a are all open. Thus, when the pump 10 is turned on and begins to rotate, there is no load on the pump 10 because fluid is able to flow to the tank 12. When the first hydraulic actuator 2 is loaded, there is no flow to the servo port a, although this port is open. With the tank port T fully open, there is no hydraulic restriction and the pump 10 operates under no load conditions. Enabling the pump 10 to start unloaded in this manner provides the same functionality as a bypass valve alone. Since all of the output flow is diverted to the reservoir 12, the hydraulic pump 10 can be increased to a minimum rotational speed, such as the rotational speed associated with a 5lpm output flow, in the first mode of operation without loading.
After pump activation, flow to the first hydraulic actuator 2 via the servo port a may be opened when the pump 10 is running at a speed corresponding to the minimum operating speed recommended by the pump manufacturer. The output stream on servo port a may be provided under two conditions. The first operating condition is that the flow demand of the first hydraulic actuator 2 is less than the minimum output flow of the pump 10, and the second operating condition is that the flow demand of the first hydraulic actuator 2 is greater than or equal to the minimum output flow of the pump 10. The spool 36 is operable under the control of the pilot signal to meet the flow requirements under both conditions.
In a second mode of operation (as shown in fig. 4) in which the pump 10 is operating at a speed corresponding to the minimum operating speed recommended by the pump manufacturer and the demanded output flow on servo port a is less than the minimum output flow, i.e. the flow is bypassed (back to port T), the total flow from the pump 10 exceeds the demand on servo port a and therefore the total flow of the pump 10 cannot be directed to servo port a.
The spool 36 is thus controlled to proportionally close the tank port T so that the desired flow is redirected to the servo port a and the excess flow continues to the tank port T. In this manner, the spool 36 operates the tank port T as a variable discharge orifice between the pressure port P and the tank port T. Proportionally closing the tank port T creates a flow distribution between ports a and T, while port P acts as an inlet or flow supply. The spool 36 may be controlled by a pilot signal to vary the degree of closure of the tank port T proportionally to the demand of the actuator.
In a second mode of operation, flow control to servo port a is between zero and the minimum output flow of the pump 10, for example from 0 to 5 LPM. This enables a creep speed of the forks (speed), wherein the actuator flow at servo port a is significantly less than the minimum required output flow (minimum rotational speed) of the pump 10, without causing pump damage. For example, the minimum rotational speed of the external gear pump at full load may be 500 RPM; the speed is set to ensure that the bearings are sufficiently lubricated to prevent damage. In a conventional forklift, a pump displacement of 23.0cc/rev may be used. At 500RPM, this would give a theoretical output flow of 11.5 LPM. If the demanded output flow at servo port a is less than 11.5LPM and the pump is caused to operate at that speed, the pump can wear out prematurely.
In the third mode of operation, the tank port T can be completely closed when the flow to the servo port a is equal to the minimum flow of the pump 10. After the demanded output flow at the servo port A is equal to or greater than the minimum output flow of the pump 10, no flow is required to the tank 12. The control algorithm of the controller will begin to control the spool 36 to proportionally convert the inlet flow provided on port P from the bypass flow to the tank port T to the actuator flow at servo port a.
After all the supply flow on the pressure port P is redirected to the servo port a and the tank port T is completely closed, the flow to the servo port a is completely controlled by the speed of the pump 10. If the flow at servo port A exceeds the minimum output flow of the pump 10, the speed of the pump 10 will be increased to increase the flow to servo port A.
In the second operating position shown in fig. 4, the spool 36 is configured such that a flow passage is defined between the pressure port P and the servo port a and the tank port T is closed. The spool 36 is controlled by the pilot signal to proportionally close the pressure port P and/or the servo port a, thereby creating a control orifice between the pump 10 and the first hydraulic actuator 2. In this way, spool 36 may be controlled to proportionally throttle flow between pressure port P and servo port A. In a fourth mode of operation, throttling of flow between pressure port P and servo port a may be performed when a flow sharing condition is required between the first hydraulic actuator 2 and one or more of the auxiliary actuators 4, 6, 8. Without throttling, the hydraulic oil supplied by the hydraulic pump will always select the path of least resistance. Thus, when the flow to the auxiliary cylinders 4, 6, 8 needs to be at a pressure exceeding the flow demand of the first actuator 2, the flow to the first actuator 2 must be throttled in order to enable the system pressure to rise to the level of the auxiliary demand pressure.
As an example, if the first actuator 2 needs 100bar to lift a loaded fork and the auxiliary cylinder 4 needs 150bar to operate the reach function, all the oil provided by the pump 10 would be directed to the lifting function of the first hydraulic actuator 2 without any flow distribution logic. This would result in an unexpected overspeeding of the lift function while the reach function would not operate at all. In most hydraulic systems, this is highly undesirable, and some flow distribution logic needs to be built into the circuit when concurrent functions are required. However, the additional components required for flow distribution performance often result in a more complex and expensive system. In a fourth mode of operation of the invention, flow distribution is achieved by throttling the flow to servo port a by the control spool 36 to raise the system pressure to the auxiliary demand pressure. In the above example, this would require a 50bar throttling application of flow to servo port a, so that the pump operates at 150bar while the supply to servo port a is 100 bar. This produces a 50bar throttling loss on the IFS spool valve 18, but enables concurrent primary and secondary functions (i.e., lift and extend) to be achieved with a single pump and without the need for complex and expensive additional valves and control systems.
In most flow distribution circuits, flow distribution is achieved by load sensing logic controlling a pilot operated logic element that can throttle the pressure differential across itself by varying the pilot signal. In a hydraulic system, there will always be a pressure drop from the outlet port of the pump to the point in the system where the load sense signal will be picked up. To counteract this pressure drop, a spring bias needs to be introduced in the logic element so that the logic element remains closed when not needed. In some systems, the biasing spring force may require up to 20 bar. Although the operation of these valves is fairly simple, they have one major drawback. To maximize system efficiency when concurrent functionality is not required, it is desirable to minimize the voltage drop across the logic elements. In the present invention, no biasing spring is required, as the valve position can be throttled directly by the spool 36 under pilot signal control. Since no biasing spring is required, the valve can be positioned to the fully open position of the valve when concurrent functions are not required, resulting in a significant increase in system efficiency.
In the second operating position, the flow direction may be reversed to provide flow from servo port a to pressure port P. Spool 36 is operable to throttle flow between pressure port P and servo port a bi-directionally, and may therefore throttle flow when flowing from servo port a to pressure port P in the same manner as described above for flow from pressure port peh actuator to port a, meaning throttling both from port P to a and from a to P.
In a fifth mode of operation, flow may be provided from the servo port a to the pressure port P to enable pressurized fluid from the first hydraulic actuator 2 to be used during descent to drive the pump 10 for energy regeneration in which the pump motor 10 operates as a hydraulic motor converting hydraulic power into mechanical shaft power. Under these conditions, it is desirable to be able to turn on the loading of the pump 10 in a controlled manner, for example if the hydraulic unit is driven by an electric motor/generator (e.g. an induction motor) with poor dynamic performance. The spool valve 18 enables the initial lowering of the fork to be achieved in a fully hydraulic manner by throttling the flow from the servo port a to the pressure port P with the spool 36. During this gravity-down phase, the rotation of the motor/generator may turn on in an unloaded manner, allowing torque to ramp up before the regenerative motor/generator unit is gradually turned on. More generally, the use of the spool valve 18 allows for improved controllability, particularly when descent at creep speeds is desired.
The pump motor 10 can be used to produce electrical energy during periods of reduced regeneration, which is stored in a battery. During a regenerative decline, kinetic energy from the hydraulic fluid pressurized by the elevated load is converted from electrical energy by driving the pump motor 10 as a generator unit. Under certain operating conditions, such as conditions where the forklift is primarily descending loaded and the lifting operation is limited, the battery may become fully charged when energy regeneration exceeds the consumption of electrical energy. After the state of charge of the battery pack is 100%, overcharge may cause damage to the battery. In this case, the down flow may be throttled such that the load is removed from the pump motor 10 to stop energy regeneration. The spool valve 18 thus provides battery overcharge protection while enabling the load to be dropped in a safe and controlled manner. In prior art arrangements, the hydraulic system required a separate logic element valve to be able to throttle flow from the servo port a to the pressure port P, again requiring additional components and increasing the complexity and cost of the system since only one-way control could be made over such a logic element valve.
In a sixth mode of operation, in the second operating position, the flow passage from the servo port a to the pressure port P may be fully open. Fully opening the flow path from the servo port a to the pressure port P minimizes the pressure drop across the spool valve 18 and maximizes system efficiency. By controlling the spool 36 so that the flow path from the servo port a to the pressure port P is in its fully open state, all of the kinetic energy available from the load can be used by the motor/generator for electrical energy recovery, which maximizes the energy saving potential compared to prior art systems.
In the third operating position, as shown in fig. 5, the spool 36 is configured such that a flow passage is defined between the servo port a and the tank port T and the pressure port P is closed. The spool 36 is controlled by the pilot signal to proportionally close the tank port T and/or the servo port a, thereby creating a control orifice between the tank 12 and the first hydraulic actuator 2. In this way, the spool 36 can be controlled to proportionally throttle flow between the servo port A and the tank port 12 during a load drop.
The third operating position provides a more conventional gravity descent mode of lowering a load without energy regeneration. During gravity descent, all available kinetic energy is converted to oil heat by controlling the orifice between the servo port a and the tank port T to cause a pressure reduction (hydraulic down) to atmospheric pressure. All flow from the first hydraulic actuator 2 goes directly to the tank 12 instead of passing through the pump 10. Although very inefficient compared to the energy recovery mode of operation, certain benefits may also be realized by gravity drop in the third operating position.
The thermal energy generated by the throttling of the flow during the gravitational fall is generally undesirable, since warming up the hydraulic oil would require a more powerful cooling system in terms of hydraulics. However, where a forklift is used in a refrigerated environment, it may be feasible to switch back to an efficient system to bring the hydraulic oil temperature into its working area as quickly as possible using the kinetic energy from the descent. If the energy recovery system is implemented in a forklift, the energy brought about by the falling load will be converted into useful electrical energy, which inherently reduces the heat transferred to the oil.
As described above, in some cases, since the battery is fully charged (charged), a reduction in the reproducibility is not feasible. Instead of throttling gravity descent and free rotation of the hydraulic pump 10 in the second operating position, the spool valve 18 may be switched to a third operating position in which the downward flow is throttled in a manner directed to the tank 12. In this manner, the pump 10 does not need to be rotated, which reduces operation of the pump 10 and minimizes system noise.
Among other advantages, the IFS valve of the present invention enables the slave cylinder to operate during descent without the need for 4 quadrat pump technology. Concurrent auxiliary functions, such as "reach" may be required during the lowering of the first hydraulic cylinder 2. The pump 10 is used during periods of reduced regeneration to capture the kinetic energy available and use that kinetic energy to charge the battery. If a concurrent auxiliary function is required during a regenerative lowering event, the load induced on the first hydraulic cylinder 2 may be used to operate the auxiliary function if the pressure is sufficient to meet the auxiliary demand. However, if insufficient pressure is caused on the first hydraulic cylinder 2, the pump 10 will be required for auxiliary function operation. It is possible to operate the pump to pressurise the pressure from the lowering cylinder by loading the return line of the pump as the lowering flow passes through the pump. However, this requires a change of pump technology from 2Q (2 quadrant) to 4Q (4 quadrant), which significantly increases cost and complexity and limits the pump technology that can be used in such energy recovery systems. In the present invention, in the event that pump operation is required to supply the auxiliary cylinder during a load drop, the spool 36 may be moved to the third position to enable flow from the first actuator 2 to the tank 12 bypassing the pump 10 and enabling the pump 10 to operate to supply the auxiliary demand.
Fig. 6 shows a simplified schematic of a hydraulic circuit 50 containing the intelligent flow distributing spool valve 18. The system includes a primary actuator cylinder C1 and a secondary actuator cylinder C2. Master cylinder C1 is a single-acting lift actuator cylinder in which the working fluid acts on only one side of the piston to lift a load. In the opposite direction, the lowering of the load is actuated by the weight of the load. The auxiliary actuator cylinder C2 is a double-acting actuator cylinder in which the working fluid acts alternately on both sides of the piston.
The system includes a powertrain (powertrain) that includes an electric motor/generator 56, a hydraulic pump/motor 58, and an energy storage device 60 (e.g., a battery). The motor/generator 56 and the pump/motor 58 may operate in a forward direction indicated by directional arrow M and in an opposite direction indicated by directional arrow G. In the forward direction M, the motor/generator 56 consumes energy from the energy storage device 60. In the opposite direction G, the motor/generator 56 is driven by the pump/motor 58 and generates electrical energy, which is discharged back into the energy storage device 60.
Hydraulic fluid flow to and from the master actuator cylinder C1 is controlled by the spool valve 18. However, while the spool valve provides the most effective and efficient means of controlling the master actuator cylinder C1, it will be appreciated that other valve means or combinations of valve means may be used. The flow of hydraulic fluid to and from the auxiliary actuator cylinder C2 is controlled by the second hydraulic control valve 62. The spool valve 18 has three ports — a pressure port P1, a servo port A1, and a return port T1. The pressure port P1 of the valve 18 is supplied by the pump/motor 58. The servo port A1 supplies the master actuator cylinder 56 and the return port T1 is connected to the hydraulic reservoir tank 12. Since the master actuator cylinder C1 is a single-acting cylinder that operates against gravity, the spool valve 18 only requires a single servo port A1. Extension of the master actuator cylinder C1 is accomplished by feeding hydraulic fluid to the master actuator cylinder C1 via the servo port a 1. Retraction of the master actuator cylinder C1 is achieved by a reverse flow through the same port a1 caused by gravity.
The second hydraulic control valve 62 has 4 hydraulic ports — a pressure port P2, a return port T2, and two controlled servo ports a2 and B2, which are required to operate the cylinders in both directions. The helper cylinder C2 has two ports 66, 68. The first port 66 is connected to a first servo port a2 and the second port 68 is connected to a second servo port. The pressure feed port P2 is supplied by the pump/motor 58, and the return port T2 is connected to the tank 12, returns to the hydraulic reservoir (T), and two controlled output ports (a2 and B2) go to the actuator C2. To extend the slave cylinder C2, fluid is supplied to the first port 66 via the first servo port a 2. Fluid flows from the second port 68 to the return port T2 via the second servo port B2. To retract the reservoir, helper cylinder C2, fluid is supplied to the second port 68 via the second servo port B2. Fluid flows from the first port 66 to the return port T2 via the first servo port A2.
The spool valve 18 and the second hydraulic control valve 62 may be proportionally controlled to vary the degree to which flow through the valves is restricted. For the spool valve 18, it is possible to proportionally restrict the flow path between the pressure port P1 and the servo port A1 for flow in both directions. It is also possible to variably restrict flow between servo port a1 and return port T1. The second hydraulic control valve 62 may be controlled to proportionally restrict flow from P2 to A2 or from P2 to B2, respectively, depending on whether the helper cylinder C2 is to be extended or retracted. The system includes provisions for determining the flow Q1 to the master cylinder C1 and the pressure PT1 required to operate the master cylinder C1. This may include data acquisition devices in the form of flow sensors 70 and pressure sensors 72. Similarly, flow sensors 74, 76 and pressure sensors 78, 80 may also be provided to determine the flow and pressure requirements of the ports of the helper cylinder C2. The motor speed required to operate the master actuator cylinder C1 and the reverse regenerative motor speed resulting from the downward flow from the master actuator cylinder C1 are indicated by the arrow directions M1 and G1, respectively. The motor speed required to operate the auxiliary cylinder C2 is represented by arrow M2. M1, G1, and M2 are combined as variables that determine the equivalent operating speed of the motor for a given function. For example, if the main actuator cylinder C1 and the auxiliary cylinder C2 are operating concurrently at a particular speed, the total motor speed M will be the product of M1 and M2, i.e., M1+ M2.
If the auxiliary function actuated by the auxiliary actuator cylinder C2 is required while the load on the main actuator cylinder C1 is dropping, the pressure generated by the load on the main actuator cylinder C1 may be used to operate the auxiliary function if the pressure is sufficient to meet the auxiliary demand. Depending on the load demand of the auxiliary actuator cylinder C2, some or all of the hydraulic power from the induced load of the main actuator cylinder C1 may be directed to the auxiliary actuator cylinder C2 to power the auxiliary actuator cylinder C2. In the event that hydraulic power exceeds the demand of auxiliary actuator cylinder C2, excess power may be directed to pump/motor 58 for electrical energy regeneration.
If the main actuator cylinder C1 is operating in the descent energy recovery mode at a lower speed G1, the total motor speed M will depend on the sum of the descent speed G1 of the main actuator cylinder C1 (which is the reverse flow through the pump) and the speed M2 of the auxiliary actuator cylinder C2. Thus, M ═ G1+ M2. If the speed M2 is greater than G1, i.e. the energy recovery flow from the main actuator cylinder C1 is less than that required by the helper cylinder C2, the motor will turn M ═ G1+ M2 in the positive direction and energy will be taken out of the battery (E +). If M2 < G1, i.e., C2 requires less flow than is being recovered from C1, the motor will rotate in the reverse direction (G), where G ═ G1+ M2.
A flow chart is provided in fig. 7, which illustrates various functional modes of operation of hydraulic system 50, as described below.
Function F1
The operator requests a single function in which the master actuator cylinder C1 (indicated as C1 in FIG. 7) needs to be extended; this will typically be a lift condition. The spool valve 18 will be fully open allowing flow from P1 to a 1. Thus, the extension speed of master actuator cylinder C1 will be directly controlled by the speed of motor/generator 56 operating as a motor and the speed of the pump/motor operating as a pump. The second hydraulic control valve 62 will be fully closed and thus prevent flow to the auxiliary actuator cylinder C2.
Energy is drawn from the battery 60 by the motor/generator 56 in a manner proportional to the speed command and the load being lifted.
Function F2
The operator requests a single function in which master actuator cylinder C1 needs to be retracted, i.e., a descent condition. The retraction speed of master actuator cylinder C1 will be directly controlled by operating motor/generator 56 as a generator and pump/motor 58 as a motor in speed control. The extension speed of the master actuator cylinder C1 will be controlled with the fluid path from a1 to P1 fully open. Without throttling, energy losses are minimized. The second hydraulic control valve 62 will be fully closed and thus prevent flow to the auxiliary actuator cylinder C2.
All of the potential energy from the descending load is regenerated into electrical energy that is proportional to the descent speed command and the magnitude of the gravity-induced, descending load. None of the potential energy is redirected elsewhere in the circuit as hydraulic power, and so this function can be considered to be full electrical energy regeneration.
Function F3
The operator requests a single function in which the auxiliary actuator cylinder C2 needs to be extended (typically an auxiliary function condition such as extend, tilt, or side shift). The extension speed of the auxiliary actuator cylinder C2 will be directly controlled by operating the motor/generator 65 as a motor and the pump/motor 58 as a pump in speed control. The spool valve 18 is controlled to be fully closed to prevent flow from P1 to A1 and the second hydraulic control valve 62 is fully open, allowing flow from P2 to A2. Also, the fully open condition minimizes energy losses. In some cases, P2 to A2 may be throttled to create sufficient back pressure for the load, which may be desirable to prevent over-load (over run) or to improve functional stability.
The energy drawn from the battery 60 is proportional to the speed command and the load being moved by the auxiliary actuator cylinder C2, as well as some potential additional throttling losses in the situation.
Function F4
The operator requests a single function in which the auxiliary actuator cylinder C2 needs to be retracted (typically an auxiliary function condition such as extend, tilt or side shift), and the speed of retraction of the main actuator cylinder will be directly controlled by operating the motor/generator 56 as a motor and the pump/motor 58 as a pump in speed control. The spool valve 18 is controlled to be fully closed to prevent flow from P1 to B1, and the second hydraulic control valve 62 is fully open, allowing flow from P2 to B2. Also, the fully open condition minimizes energy losses. In some cases, P2 through B2 may be throttled to create sufficient back pressure for the load, which may be desirable to prevent load overrun or improve functional stability.
Function F5
The operator requests a dual, concurrent function in which both the main actuator cylinder C1 and the auxiliary actuator cylinder C2 need to be extended. This will typically be a lift condition with an auxiliary function such as reach, tilt or side shift. The valve control will depend on the load conditions induced on the main actuator cylinder C1 and the auxiliary actuator cylinder C2.
If the load on the main actuator cylinder C1 is lower than the load induced on the auxiliary actuator cylinder C2 (PT1 < PT2), the spool valve 18 is throttled from P1 to A1 to create sufficient back pressure to operate the concurrent function. If this is not the case, the oil will take the path of least resistance, which results in the auxiliary actuator cylinder C2 not being able to operate and the main actuator cylinder C1 being overrun faster than the input command.
The second hydraulic control valve 62 is controlled to be fully opened (P2 to a2) to minimize energy loss. If desired, P2 through A2 may be throttled to create sufficient back pressure for the load, e.g., to prevent load overrun or improve functional stability.
The speeds of the main actuator cylinder C1 and the auxiliary actuator cylinder C2 will be controlled as a result of operating the motor/generator 56 as a motor and the pump/motor 58 as a pump in speed control. The total speed M of the motor 56 will be a combination of both the part speed commands M1 and M2, so M1+ M2.
If M1+ M2 remains below the maximum allowable speed at which the pump/motor 58 operates, then both functions C1 and C2 will operate at the requested speed. In the event that M1+ M2 exceeds this maximum speed, priority will be given to either the master actuator cylinder C1 or the auxiliary actuator cylinder C2 by changing the throttle command on the spool valve 18. Typically, but not necessarily, the auxiliary actuator cylinder C2 will be treated preferentially, which means that the speed of the auxiliary actuator cylinder remains unaffected. This operation may be referred to as flow distributed lift with throttled lift operation.
The energy drawn from the battery 60 is proportional to the combined speed command and the load being moved by the main and auxiliary actuator cylinders C1 and C2, as well as some potential additional throttling losses in the situation.
Function F6
The operator requests a dual concurrent function where both the main actuator cylinder C1 and the auxiliary actuator cylinder C2 require extension, i.e., a lift condition along with an auxiliary function condition such as extend, tilt, or side-shift. The valve control will depend on the load conditions induced on the main actuator cylinder C1 and the auxiliary actuator cylinder C2.
If the load on the primary actuator cylinder C1 is higher than or equal to the load induced on the secondary actuator cylinder C2 (PT1> -PT 2), the second hydraulic control valve 62 is throttled from P2 to A2 to create sufficient back pressure to operate the concurrent function. If this is not the case, the oil will take the path of least resistance, which results in C1 being inoperable and the auxiliary actuator cylinder C2 being overrun faster than the input command.
The spool valve 18 is controlled to be fully open (P1 to a1) to minimize energy loss. P1 to Al may be throttled to create sufficient back pressure for the load if desired, for example, if necessary to prevent load overrun or improve functional stability.
The speed of the master actuator cylinder C1 and the auxiliary actuator cylinder C2 will be controlled by operating the motor/generator 56 as a motor and the pump/motor 58 as a pump in speed control. The total speed of motor M will be a combination of both partial speed commands M1 and M2, so M1+ M2. If M1+ M2 remains below the maximum allowable speed for P/M operation, then both functions C1 and C2 will operate at the requested speed. In the event that M1+ M2 exceeds this maximum speed, priority will be given to either the master actuator cylinder C1 or the auxiliary actuator cylinder C2 by changing the throttle command on the spool valve 18. Typically, but not necessarily, the auxiliary actuator cylinder C2 will be treated preferentially, which means that the speed of the auxiliary actuator cylinder remains unaffected. This operation may be referred to as flow-distributed lift with throttled auxiliary operation.
The energy drawn from the battery 60 is proportional to the combined speed command and the load being moved by the main and auxiliary actuator cylinders C1 and C2, as well as some potential additional throttling losses in the situation.
Function F7
In the case where the operator requests dual (concurrent) functionality, where the main actuator cylinder C1 needs to be extended and the auxiliary actuator cylinder C2 needs to be retracted, a lift condition along with an auxiliary function condition such as extend, tilt, or side-shift. The valve control will depend on the load conditions induced on the main actuator cylinder C1 and the auxiliary actuator cylinder C2.
If the load on the main actuator cylinder C1 is lower than the load induced on the auxiliary actuator cylinder C2 (PT1 < PT3), the spool valve 18 is throttled from P1 to A1 to create sufficient back pressure to operate the concurrent function. If this is not the case, the oil will take the path of least resistance, which results in the auxiliary actuator cylinder C2 not being able to operate and the main actuator cylinder C1 being overrun faster than the input command.
The second hydraulic control valve 62 is controlled to be fully opened (P2 to B2) to minimize energy loss. If desired, P2 through B2 may be throttled to create sufficient back pressure for the load, for example if it is desired to prevent load overrun or improve functional stability.
The speed of the master actuator cylinder C1 and the auxiliary actuator cylinder C2 will be controlled by operating the motor/generator 56 as a motor and the pump/motor 58 as a pump in speed control. The total speed of motor M will be a combination of both partial speed commands M1 and M2, so M1+ M2. If M1+ M2 remains below the maximum allowable speed at which the pump/motor 58 operates, then both functions C1 and C2 will operate at the requested speed. In the event that M1+ M2 exceeds this maximum speed, priority will be given to either the master actuator cylinder C1 or the auxiliary actuator cylinder C2 by changing the throttle command on the spool valve 18. Typically, but not necessarily, the auxiliary actuator cylinder C2 will be treated preferentially, which means that the speed of the auxiliary actuator cylinder remains unaffected. This operation may be referred to as flow distributed lift with throttled lift operation.
The energy drawn from the battery 60 is proportional to the combined speed command and the load being moved by the main and auxiliary actuator cylinders C1 and C2, as well as some potential additional throttling losses in the situation.
Function F8
The operator requests a dual concurrent function in which the main actuator cylinder C1 needs to be extended and the auxiliary actuator cylinder C2 needs to be retracted, i.e., a lift condition along with an auxiliary function condition such as extend, tilt, or side-shift. The valve control will depend on the load conditions induced on the main actuator cylinder C1 and the auxiliary actuator cylinder C2.
If the load on the primary actuator cylinder C1 is higher than or equal to the load induced on the secondary actuator cylinder C2 (PT1> -PT 3), the second hydraulic control valve 62 is throttled from P2 to B2 to create sufficient back pressure to operate the concurrent function. If this is not the case, the oil will take the path of least resistance, which results in the master actuator cylinder C1 being inoperable and the auxiliary actuator cylinder C2 being overrun faster than the input command.
The spool valve 18 is controlled to be fully open (P1 to a1) to minimize energy loss. P1 to Al may be throttled to create sufficient back pressure for the load, e.g., to prevent load overrun or improve functional stability. The speed of the master actuator cylinder C1 and the auxiliary actuator cylinder C2 will be controlled by operating the motor/generator 56 as a motor and the pump/motor 58 as a pump in speed control. The total speed of motor M will be a combination of both partial speed commands M1 and M2, so M1+ M2. If M1+ M2 remains below the maximum allowable speed at which the pump/motor 58 operates, then both functions C1 and C2 will operate at the requested speed. In the event that M1+ M2 exceeds this maximum speed, priority will be given to either the master actuator cylinder C1 or the auxiliary actuator cylinder C2 by changing the throttle command on the spool valve 18. Typically, but not necessarily, the auxiliary actuator cylinder C2 will be treated preferentially, which means that the speed of the auxiliary actuator cylinder remains unaffected. This operation may be referred to as flow-distributed lift with throttled auxiliary operation.
The energy drawn from the battery 60 is proportional to the combined speed command and the load being moved by the main and auxiliary actuator cylinders C1 and C2, as well as some potential additional throttling losses under the circumstances.
Function F9
The operator requests a dual concurrent function in which the main actuator cylinder C1 needs to be retracted and the auxiliary actuator cylinder C2 needs to be extended, i.e., a descent condition along with an auxiliary function condition such as extend, tilt, or side-shift. The valve control will depend on the load conditions induced on the main actuator cylinder C1 and the auxiliary actuator cylinder C2.
If the load on the main actuator cylinder C1 is lower than the load caused on the auxiliary actuator cylinder C2 (PT1 < PT2 or PT1 < PT3), the load on the main actuator cylinder C1 is insufficient to feed the auxiliary actuator cylinder C2. In this situation, the system will revert to a "conventional hydraulic system" in which the induced load from the main actuator cylinder C1 is throttled and diverted to the storage tank 12. This is commonly referred to as gravity descent and is achieved by proportional control of the spool valve (ports a1 to T1). All the potential energy caused is converted into oil heat. The auxiliary actuator cylinder C2 is controlled as described in functions F3 and F4, depending on whether the auxiliary actuator cylinder C2 is being extended (F3) or retracted (F4). The energy drawn from the battery 60 is proportional to the combined speed command and the load being moved by the auxiliary actuator cylinder C2, as well as some potential additional throttling losses in the situation. The load and speed of the master actuator cylinder C1 do not affect the energy consumption/regeneration through the electro-hydraulic powertrain. Instead, the potential energy induced on the master actuator cylinder C1 will be relieved through the spool valve 18 to the reservoir, wasting all of the energy into the heat of the hydraulic oil. This operation may be referred to as flow-distributed descent with gravity descent.
Functions F10 to F12
The operator requests a dual concurrent function in which the main actuator cylinder C1 needs to be retracted and the auxiliary actuator cylinder C2 needs to be extended, i.e., a descent condition along with an auxiliary function condition such as extend, tilt, or side-shift. The valve control will depend on the load conditions induced on the main and auxiliary actuator cylinders C1 and C2 and the speed commands for the main and auxiliary actuator cylinders C1 and C2.
If the load on the primary actuator cylinder C1 is higher than or equal to the load induced on the secondary actuator cylinder C2 (PT1> -PT 2), the second hydraulic control valve 62 is throttled from P2 to A2 to create sufficient back pressure to controllably operate the concurrent function. If this is not the case, oil will flow "uncontrolled" from the main actuator cylinder C1 into the auxiliary actuator cylinder C2, and if the loads incurred are significantly different, this can cause the C2 to operate dangerously and too quickly. The spool valve 18 is controlled to be fully open (a1 to P1) to minimize energy loss.
The speeds of the main actuator cylinder C1 and the auxiliary actuator cylinder C2 will be controlled by operating the motor/generator 56 as a generator and the pump/motor 58 as a motor in speed control. The total speed of motor M will be the combination of the part speed commands G1 and M2, so M is G1+ M2. When PT1 is greater than PT2, there are 3 cases for the speed control.
Function F10
In a first option, the retraction speed G1 of the main actuator cylinder C1 is lower than the extension speed M2 of the auxiliary actuator cylinder C2. Although the resulting pressure is sufficient to feed the C2 directly, it will affect the C2 extension speed because the master actuator cylinder C1 retraction speed command is too slow. Thus, the control system may revert to a conventional system in which the spool valve 18 is used to throttle the load from A1 to T1 and waste energy as heat. This may be referred to as flow allocation with temporary hydraulic energy waste.
Alternatively, in the second option, the resulting pressure and flow from the master actuator cylinder C1 (i.e., C1 power) may be used to directly drive the auxiliary actuator cylinder C2. In this case, the second hydraulic control valve 62 is throttled (P2 to a2), and the spool valve 18 is fully opened (a1 to P1) to maximize energy regeneration. This operation may be referred to as flow distribution with 100% hydraulic energy recovery.
The choice of the first or second option depends on the end user and both can be performed using the same hardware. The second option would be preferred if energy saving is most critical. However, if productivity is of paramount importance, then the first alternative would be a better choice. It is also possible to change the control algorithm "on-the-fly" depending on the state of charge of the battery.
In a first option, energy will be drawn from the battery 60 in a manner proportional to the speed command and the load being moved by the auxiliary actuator cylinder C2, as well as some potential additional throttling losses in the situation. The Cl load and speed do not affect energy consumption/regeneration through the electro-hydraulic powertrain, and the motor/generator 56 operates as a motor, driving the P/M as a pump (P).
In the second option, when the load and speed induced on the main actuator cylinder C1 is fed directly to the auxiliary actuator cylinder C2, no energy will be drawn from the battery 60, but the auxiliary actuator cylinder C2 will run slower than usual. Motor/generator 56 is not used to drive C2. This operation is referred to as flow-distributed descent with limited auxiliary speed operation and 100% hydraulic energy recovery.
Function F11
This function relates to the case where the retraction speed G1 of the main actuator cylinder C1 is equal to the extension speed M2 of the auxiliary actuator cylinder C2. In this situation, hydraulic power from the main actuator cylinder C1 is transferred directly to the auxiliary actuator cylinder C2. The auxiliary actuator cylinder C2 is actuated entirely by hydraulic power from the main actuator cylinder C1. No energy is drawn from the battery 60 because the load and velocity induced on the main actuator cylinder C1 directly matches and feeds the velocity of the auxiliary actuator cylinder C2. The second hydraulic control valve 62 may provide some throttling to match the two loads and prevent overrun. The motor/generator 56 is used to drive neither the retraction speed of the main actuator cylinder C1 nor the extension speed of the auxiliary actuator cylinder C2. The retraction speed of the master actuator cylinder C1 is controlled by throttling through the second hydraulic control valve 62 for the extend C2.
This function is called flow-distributed descent with perfectly matched speed assist operation and 100% hydraulic energy recovery.
Function F12
This function relates to the case where the retraction speed G1 of the main actuator cylinder C1 is greater than the extension speed M2 of the auxiliary actuator cylinder C2. In this situation, hydraulic power from the main actuator cylinder C1 is again directly transferred to the auxiliary actuator cylinder C2. The auxiliary actuator cylinder C2 is actuated entirely by hydraulic power from the main actuator cylinder C1. When the load and speed induced on the master actuator cylinder C1 exceeds the power demand of the auxiliary actuator cylinder C2, no energy is drawn from the battery 60. The speed of the auxiliary actuator cylinder C2 is controlled by throttling the second hydraulic control valve 62, which directs hydraulic fluid directly from the main actuator cylinder C1 into the auxiliary actuator cylinder C2, which is the hydraulic energy recovery portion of operation. The speed of the master actuator cylinder C1 exceeds the extension or retraction speed of the master actuator cylinder C2. Accordingly, excess hydraulic fluid not required by auxiliary actuator cylinder C2 is directed to pump/motor 58 to drive motor/generator 56 as a generator to regenerate electrical energy, which is stored in battery 60.
This function is referred to as flow-split descent with combined/hybrid electrical and hydraulic energy recovery.
The control algorithm of the hydraulic system controller continuously monitors command requests from the operator and the system operating conditions of the main actuator cylinder C1 and the auxiliary actuator cylinder C2. The controller can be programmed to make intelligent decisions to switch between the above functions to optimize energy efficiency or productivity based on the available load. The controller is able to switch between different modes of operation "on the fly". For example, the operator may begin lowering the load in a single operation corresponding to F2. Subsequently, a secondary instruction may be added. Depending on the load on the master actuator cylinder C1, the controller will switch to function F9 or F10/F11/F12 based on the speed command. This would require function F10 if, for example, the operator provided a slow main actuator cylinder C1 retract command and a fast auxiliary actuator cylinder C2 extend command. Once the master actuator cylinder C1 retract speed command increases, the system may switch to F11 and F12 if desired. If the auxiliary actuator cylinder C2 reaches the end of stroke, the auxiliary actuator cylinder C2 command becomes invalid and the system will revert to function F2. During all of these command and control algorithm function switches, retraction of the auxiliary actuator cylinder C1 is consistent, but the energy flow path has switched from full electrical energy recovery (F2) to full hydraulic energy recovery (F10/F11), to hybrid electrical and hydraulic energy recovery (F12), back to full electrical energy recovery (F2).

Claims (24)

1. A hydraulic system for a load handling vehicle, the system comprising
A hydraulic lift actuator arranged and configured to operate in a load lift mode and a load down mode in which a main hydraulic actuator provides hydraulic power P1 to the hydraulic system;
at least one auxiliary hydraulic actuator having a hydraulic power demand P2 when operated;
a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator;
wherein the hydraulic system is configured such that when the hydraulic lifting actuators are in load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than or equal to P2, hydraulic power can be directed from the hydraulic lifting actuators directly to the at least one auxiliary hydraulic actuator such that the at least one auxiliary hydraulic actuator is directly actuated by hydraulic power from the hydraulic lifting actuators.
2. The hydraulic system of claim 1, wherein the hydraulic pump is a hydraulic pump/motor and is arranged to receive hydraulic power from the hydraulic lifting actuator when the hydraulic lifting actuator is in the load-lowering mode.
3. The hydraulic system of claim 2, further comprising a motor/generator and an electrical storage device, and the motor/generator is connected to the hydraulic pump/motor such that: in a drive mode, the motor/generator operates as a motor to power the pump/motor and the pump/motor operates as a pump, and in a regeneration mode, the pump/motor operates as a motor and drives the motor/generator to operate as a generator to generate electricity, which is supplied to an energy storage device.
4. The hydraulic system of claim 3, wherein the hydraulic system is configured such that when the hydraulic lifting actuators are in a load-lowering mode and at least one auxiliary hydraulic actuator needs to be actuated concurrently, and P1 is greater than P2, excess hydraulic power not needed by the at least one auxiliary hydraulic actuator can be directed to drive the pump/motor in a regeneration mode.
5. The hydraulic system of claim 3 or 4, wherein the hydraulic system further comprises a reservoir tank and is configured such that when hydraulic lifting actuators are in load-down mode and at least one auxiliary hydraulic actuator needs to be actuated concurrently, and P1 is greater than P2 and regeneration is not needed, excess hydraulic flow from the hydraulic lifting actuators that is not needed for the at least one auxiliary actuator is directed directly to the reservoir tank such that the hydraulic flow bypasses hydraulic pump/motors.
6. The hydraulic system of claim 3 or 4, wherein the hydraulic system further comprises a reservoir tank and is configured such that when hydraulic lift actuators are in a load-down mode and require concurrent actuation of at least one hydraulic actuator, and P1 is less than P2, hydraulic flow from the hydraulic lift actuators is directed directly to the reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor, and the hydraulic pump/motor operates in a drive mode to actuate the at least one hydraulic actuator.
7. The hydraulic system of claim 6, further comprising a lift valve arranged to control hydraulic fluid flow to and from the hydraulic lift actuator, wherein the lift valve is operable to variably restrict fluid flow from the hydraulic lift actuator to the reservoir tank when hydraulic flow from the hydraulic lift actuator is directed directly to the reservoir tank, thereby controlling a rate of descent of the hydraulic lift actuator.
8. The hydraulic system of any one of claims 3 to 7, wherein when the hydraulic lift actuators are in a load-lowering mode and operation of the at least one auxiliary hydraulic actuator is not required, all of the hydraulic power P2 is directed to drive the pump/motor in the regenerative mode.
9. The hydraulic system of any preceding claim, wherein when it is desired to concurrently operate the hydraulic lifting actuator in the load lifting mode and operate the at least one helper cylinder, both the hydraulic lifting actuator and the at least one helper cylinder are driven by a pump/motor which operates as a pump in the drive mode.
10. The hydraulic system of claim 9, further comprising a lift valve for controlling flow to and from the hydraulic lift actuator and an auxiliary valve for controlling flow to and from the auxiliary hydraulic actuator, wherein when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and a load on the hydraulic lift actuator is greater than a load on the auxiliary hydraulic actuator, the auxiliary valve is throttled to create sufficient back pressure to enable the hydraulic lift actuator to operate concurrently with the auxiliary hydraulic actuator.
11. The hydraulic system of claim 9 or 10, wherein when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and the combined speed of the hydraulic lift actuator and the auxiliary hydraulic actuator exceeds the maximum speed of the pump/motor, operation of one of the hydraulic lift actuator and the auxiliary hydraulic actuator is prioritized and allowed to continue at a desired speed while throttling flow to the other to reduce the combined speed to a level equal to or below the speed range of the pump/motor.
12. The hydraulic system of any preceding claim, wherein when the hydraulic lift actuators are in a load-lowering mode and concurrent actuation of at least one auxiliary hydraulic actuator is required, and P1 is greater than P2, but the lowering speed of the hydraulic lift actuators is less than the demanded speed of the auxiliary hydraulic actuator, hydraulic flow from the hydraulic lift actuators can be directed directly to the reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor, and the hydraulic pump/motor operates in a drive mode to actuate the at least one hydraulic actuator.
13. A load handling vehicle comprising a hydraulic system according to any preceding claim.
14. A method of operating a hydraulic system for a load handling vehicle, the hydraulic system comprising a hydraulic lifting actuator arranged and configured to operate in a load lifting mode in which a load is induced on the actuator and in a load lowering mode in which a main hydraulic actuator provides hydraulic power P1 to the hydraulic system, at least one hydraulic actuator having a hydraulic power demand P2 when operating, and a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator;
wherein when the hydraulic lift actuators are in a load-lowering mode and concurrent actuation of at least one auxiliary hydraulic actuator is required, and P1 is greater than or equal to P2, the method comprises actuating the at least one auxiliary hydraulic actuator by directing hydraulic power from the hydraulic lift actuators directly to the at least one auxiliary hydraulic actuator such that the at least one auxiliary hydraulic actuator is fully actuated by hydraulic power from the hydraulic lift actuators.
15. The method of claim 14, further comprising: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than P2, excess hydraulic power not required by the at least one auxiliary hydraulic actuator is directed to drive the pump/motor in a regenerative mode to generate electricity.
16. The method of claim 15, further comprising: when the hydraulic lift actuators are in a load-down mode and at least one auxiliary hydraulic actuator needs to be actuated concurrently, and P1 is greater than P2 and electrical regeneration is not needed, directing excess hydraulic flow from the hydraulic lift actuators that is not needed for the at least one auxiliary actuator directly to a reservoir tank so that the hydraulic flow bypasses a hydraulic pump/motor reservoir tank.
17. The method according to claim 15 or 16, further comprising: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one hydraulic actuator, and P1 is less than P2, directing hydraulic flow from the hydraulic lift actuators directly to a reservoir tank such that the hydraulic flow bypasses the hydraulic pump/motor and operating the hydraulic pump/motor in a drive mode to actuate the at least one hydraulic actuator.
18. The method of claim 17, further comprising: operating the lift valve to variably restrict fluid flow from the hydraulic lift actuator to the reservoir tank when hydraulic flow from the hydraulic lift actuator is directed directly to the reservoir tank to control a rate of descent of the hydraulic lift actuator
19. The method according to any one of claims 16 to 18, further comprising: when the hydraulic lift actuator is in the load-down mode and operation of the at least one auxiliary hydraulic actuator is not required, all hydraulic power P2 is directed to drive the pump/motor in the regeneration mode.
20. The method according to any one of claims 15 to 19, comprising: wherein when it is desired to concurrently operate the hydraulic lifting actuator in a load lifting mode and operate at least one auxiliary cylinder, the pump is operated in a drive mode to drive both the hydraulic lifting actuator and the at least one auxiliary cylinder.
21. The method of claim 20, wherein the hydraulic system includes a lift valve for controlling flow to and from a hydraulic lift actuator and an auxiliary valve for controlling flow to and from an auxiliary hydraulic actuator, and the method comprises: throttling the auxiliary valve to create sufficient back pressure to enable the hydraulic lift actuator to operate concurrently with the auxiliary hydraulic actuator when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and a load on the hydraulic lift actuator is greater than a load on the auxiliary hydraulic actuator
22. A method according to claim 20 or 21, comprising: when the hydraulic lift actuator and the auxiliary hydraulic actuator are being driven concurrently by the pump/motor and the combined speed of the hydraulic lift actuator and the auxiliary hydraulic actuator exceeds the maximum speed of the pump/motor, prioritizing operation of one of the hydraulic lift actuator and the auxiliary hydraulic actuator and allowing said prioritizing operation to continue at a desired speed and simultaneously throttling flow to the other to reduce the combined speed to a level equal to or below the speed range of the pump/motor.
23. The method according to any one of claims 15 to 22, comprising: when the hydraulic lift actuators are in a load-down mode and it is desired to concurrently actuate at least one auxiliary hydraulic actuator, and P1 is greater than P2, but the rate of descent of the hydraulic lift actuators is less than the rate required by the auxiliary hydraulic actuator, directing hydraulic flow from the hydraulic lift actuators directly to the reservoir tank so that the hydraulic flow bypasses the hydraulic pump/motor, and operating the hydraulic pump/motor in a drive mode to actuate the at least one hydraulic actuator.
24. A hydraulic system for a load handling vehicle, the system comprising
A hydraulic lift actuator arranged and configured to operate in a load-lifting mode and a load-lowering mode in which a load is induced on the hydraulic lift actuator;
at least one auxiliary hydraulic actuator having a pressure demand when operated; and
a hydraulic pump arranged to direct hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator;
wherein the hydraulic system is configured such that, when the hydraulic lifting actuators are in a load lowering mode and concurrent actuation of at least one auxiliary hydraulic actuator is required, the resulting pressure on the hydraulic lifting actuators can be used to operate the at least one auxiliary hydraulic actuator if the resulting pressure is greater than or equal to the required pressure.
CN201980057452.4A 2018-07-11 2019-07-11 Hydraulic system for load handling vehicle Pending CN112654579A (en)

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GB1811366.2A GB2575480A (en) 2018-07-11 2018-07-11 A control valve assembly for a load handling vehicle
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PCT/EP2019/068769 WO2020011959A1 (en) 2018-07-11 2019-07-11 A hydraulic system for a load handling vehicle

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EP3820807A1 (en) 2021-05-19
US20210270293A1 (en) 2021-09-02

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